For any fireman, as defined in this Article, who has filed an application for appointment as a member of the fire department of the city, the age therein stated shall be conclusive evidence of his age for the purposes of providing all benefits under this Article. However, for any fireman, as defined in this Article, entering service with the City of Chicago Fire Department after January 1, 2020, the actual birthdate as provided in the fireman’s birth certificate shall be conclusive evidence of the fireman’s age for the purposes of this Article.